The IMTA-cultivated Chlorophyta Ulva spp. as a sustainable ingredient in Nile tilapia (Oreochromis niloticus) diets

Increasing levels of a mixture of Ulva spp. produced in an integrated multi-trophic aquaculture (IMTA) system were evaluated in Nile tilapia juveniles for partial replacement of dietary fish meal. A control diet (CTRL) was compared with three experimental diets containing 10 % (U10), 15 % (U15), and 20 % (U20) of Ulva spp. meal. Triplicate groups of fish (13 g initial body weight) were fed each diet for 63 days at 26 °C. Nutrient apparent digestibility coefficients and nitrogen retention efficiency did not vary significantly among diets. By the end of the trial, all groups of fish more than tripled their initial body weight. Specific growth rate and final body weight of U10 diet were similar to CTRL and significantly higher than U15 and U20 diets. Increasing Ulva dietary incorporation levels significantly increased feed conversion ratio (FCR), from 1.0 (CTRL) to 1.4 (U20). Fish fed with U10 diet had the highest protein efficiency ratio and nitrogen retention efficiency allowing this fish to growth and reach a final body weight similar to the CTRL group. Protein content was highest in fish fed with the CTRL diet, whereas the highest lipid content was observed in fish fed with U20 diet. The results show that the incorporation of IMTA-produced Ulva meal in Nile tilapia diets is possible up to 10 % without compromising growth performance, protein utilization, and protein retention of juveniles. The high capacity of Nile tilapia to digest all experimental diets suggests that Ulva meal is a practical partial replacement for fish meal in Nile tilapia diets.     

Growth performance and body composition in response to dietary protein and lipid levels in Nile tilapia (Oreochromis niloticus Linnaeus, 1758) subjected to normal and temporally restricted feeding regimes

A factorial experiment was designed to examine the effect on compensatory growth (CG) of Nile tilapia Oreochromis niloticus fed diets containing different protein and lipid levels under normal and temporally restricted feeding regimes. Four diets were formulated to contain either 30% or 36% crude protein, and 5% or 11% crude lipid. Triplicate replicates of each treatment were assigned to 24 150‐L tanks (20 fish/tank density). Fish (mean initial weight ± SD = 8.79 ± 0.34 g) were then fed either the normal feeding regime (thrice daily to apparent satiation) or the restricted regime (1 day feed deprivation followed by 3 days of feeding to apparent satiation) over a 44‐days study period. Fish receiving a diet under the restricted regime achieved weight gains (WG) comparable to fish consuming the diet containing 30% protein and 5% lipids under the normal feeding regime. Fish maintained on the restricted feeding regime exhibited reduced feed intake (FI), WG, feed efficiency ratio (FE), protein efficiency rate (PER) and hepatosomatic index versus fish on the normal feeding regime, except WG in fish fed the diet with 30% protein and 5% lipids. However, the resultant FI (85%~94%) was higher than the excepted 75% intake when fish were subjected to the restricted regime. Feeding 11% lipid diets led to improved FI, WG, FE, and PER compared to feeding the 5% lipid diets. Increased FI, WG, and FE, but reduced PER were observed in fish fed with 36% protein versus fish fed 30% protein. Fish receiving the 36% protein diets had lower whole‐body moisture and ash contents, but elevated whole‐body protein and lipid contents compared to those receiving the 30% protein diets. Whole‐body moisture contents were lower, but whole‐body protein, lipid and ash contents were higher in fish fed 11% lipid diets than in fish fed 5% lipid diets. There was an increase in whole‐body moisture content, but a decrease in protein and lipid content in response to the restricted feeding regime. Ash content was not affected by the feeding regime. The present study shows that Nile tilapia fed diets subjected to a restricted feeding regime exhibited growth comparable to those fed the diet at 30% protein and 5% lipid levels under a normal feeding regime. This positive effect was more pronounced in diets at a high protein level or in a combination of high protein and lipid levels.     

Dietary lipid sources affect cold tolerance of Nile tilapia (Oreochromis niloticus)

This study was carried out to evaluate the effects of dietary lipid sources on growth performance, fatty acids composition and cold tolerance of Nile tilapia (Oreochromis niloticus) fingerlings (7.00 ± 0.50 g/fish). The fish were fed four isonitrogenous (28% crude protein), isocaloric (500 kcal/100 g) diets containing four lipid sources; fish oil (FO), corn oil (CO), coconut oil (COCO) or fish oil/ corn oil mixture (1:1 ratio) (oil mix). The diets were offered to the fish at a daily rate of 3% of their body weights (BW), twice a day for two months. After the feeding trial, the fish were exposed to decreasing water temperature from 25 °C until the appearance of death symptoms. The results revealed that FO-based diets (FO and oil mix) produced the best growth rates and feed efficiency, followed by corn oil diet, while COCO resulted in the lowest performance. Fish fed on CO and oil mix showed higher body unsaturated fatty acids (UFA) and lower lethal temperature than those fed on FO- or COCO-based diets. These results indicate that cold shock can modify the lipid metabolism in Nile tilapia by lowering total body saturated fatty acids and raising n-6 and n-3 UFA. This finding suggests that the inclusion of high levels of plant oils in Nile tilapia feeds can enhance their cold tolerance.     

Nutritional evaluation of fermented black gram (Phaseolus mungo) seed meal in compound diets for rohu, Labeo rohita (Hamilton), fingerlings

Six isonitrogenous (approximately 35% crude protein) and isocaloric (approximately 4.0 kcal g⁻¹) diets were formulated incorporating raw and fermented black gram, Phaseolus mungo, seed meal at 20%, 30% and 40% levels by weight into a fishmeal‐based control diet fed to rohu, Labeo rohita, fingerlings (mean weight, 1.81 ± 0.21 g) for 80 days for a study of fish performance. A particular bacterial strain (Bacillus sp.) isolated from the intestine of adult common carp (Cyprinus carpio) reared in the wild having significant amylolytic, cellulolytic, lipolytic and proteolytic activities was used for fermentation of seed meal for 15 days at 37 ± 2°C. Fermentation of P. mungo seed meal was effective in significantly reducing the crude fibre content and antinutritional factors such as tannins and phytic acid, and enhancing available free amino acids and fatty acids. In terms of growth, feed conversion ratio and protein efficiency ratio, the 30% fermented black gram seed meal incorporated diet resulted in a significantly (P < 0.05) better performance of rohu fingerlings. In general, growth and feed utilization efficiencies of diets containing fermented seed meal were superior to diets containing raw seed meal. The apparent protein digestibility (APD) values decreased with increasing levels of raw seed meal in the diets. The APD for raw seed meal was lower at all levels of inclusion in comparison to those for the fermented seed meals. The maximum deposition of protein in the carcass was recorded in fish fed the diet containing 40% fermented seed meal. The results indicate that fermented black gram seed meal can be incorporated in carp diets up to the 30% level compared to the 10% level of raw seed meal.     

Effect of dietary fish meal replacement by red algae, Gracilaria arcuata, on growth performance and body composition of Nile tilapia Oreochromis niloticus

A 12-week long feeding experiment was initiated to evaluate the effect of dietary supplementation of red algae, Gracilaria arcuata, on the growth performance, feed utilization and body composition of Nile tilapia Oreochromis niloticus (Linnaeus, 1758). The fish were fed with an algae-free control diet (C) and three experimental diets which replaced conventional fish meal with varying levels of dried G. arcuata (20%, 40% and 60%, represented as G20, G40 and G60, respectively). The growth parameters of final weight (FW), weight gain (WG), percentage of weight gain (WG%), daily growth rate (DGR) and specific growth rate (SGR) were significantly reduced (P < 0.05) at all levels of algae incorporation compared to the control diet. Moreover, the negative impact of Gracilaria meal on the growth performance of Nile tilapia increased as the proportion of algae in the diet increased, with fish on diet G20 exhibiting a significantly higher growth performance than the fish on either of the G40 and G60 diets. On the other hand, the feed utilization parameters feed conversion ratio (FCR) and protein efficiency ratio (PER) did not show significant differences between the fish in the control group and those on diet G20, although poorer FCR and PER outcomes were achieved in the case of fish on diet G60. The content of moisture, protein and ash in muscle and carcass increased as the proportion of Gracilaria meal in the diets increased, but the reverse was true for lipid level. These results indicate that incorporation of less than 20% red algae, Gracilaria arcuata, could be feasible in the diet of Nile tilapia and further studies are recommended to optimize the level of algae to improve growth performance.     

Improvement of nutritive value of grass pea (Lathyrus sativus) seed meal in the formulated diets for rohu, Labeo rohita (Hamilton) fingerlings after fermentation with a fish gut bacterium

Eight isonitrogenous (35% crude protein approximately) and isocaloric (4.0 kcalg(-1) approximately) diets were formulated incorporating raw and fermented grass pea (Lathyrus sativus) seed meal at 10%, 20%, 30% and 40% levels by weight into a fish meal based diet and fed to rohu, Labeo rohita, fingerlings for 80 days and fish performance was studied. A particular bacterial strain (Bacillus sp.) isolated from the intestine of adult common carp (Cyprinus carpio) reared in the wild having significant amylolytic, cellulolytic, lipolytic and proteolytic activities were used for fermentation of seed meal for 15 days at 37 degrees C. Fermentation of grass pea seed meal was effective in significantly reducing the crude fibre content and anti-nutritional factors, such as tannins, phytic acid and the neurotoxin, beta-ODAP and enhancing the available free amino acids and fatty acids. In terms of growth response, feed conversion ratio and protein efficiency ratio, 30% fermented grass pea seed meal incorporated diet resulted in significantly (P < 0.05) better performance of rohu fingerlings. In general, growth and feed utilization efficiencies of fish fed diets containing fermented seed meal were superior to those fed diets containing raw seed meal. The apparent protein digestibility (APD) values decreased with increasing levels of raw seed meal in the diets. The APD for raw seed meal was lower at all levels of inclusion in comparison to those for the fermented seed meals. The highest deposition of carcass protein was recorded in fish fed the diet containing 40% fermented seed meal. The results indicated that fermented grass pea seed meal can be incorporated in carp diets up to 30% level compared to 10% level of raw seed meal.     

Lysine and arginine requirements of juvenile Asian sea bass (Lates calcarifer)

Two separate experiments were conducted to determine the dietary requirements of juvenile Asian sea bass Lates calcarifer Bloch for lysine and arginine. Fish (average initial weight: lysine experiment, 13.12 ± 0.12 g; arginine experiment, 2.56 ± 0.13 g) were given amino acid test diets for 12 weeks containing fish meal, zein, squid meal, and crystalline amino acids. Each set of isonitrogenous and isocaloric test diets contained graded levels of L ‐lysine or L ‐arginine. The feeding rate in the lysine experiment was at 4–2.5% of the body weight day^?1, while in the arginine experiment it was at 10–4% of the body weight day^?1. The fish (20 per tank, lysine experiment; 15 per tank, arginine experiment) were reared in 500‐L fibreglass tanks with continuous flowthrough sea water at 27 °C and salinity of 31 ppt in the lysine experiment and at 29 °C and salinity of 29 ppt in the arginine experiment. The experiments were in a completely randomized design with two replicates per treatment. Survival was high in fish given adequate lysine or arginine. Mean percentage weight gains were significantly different in fish fed varying levels of lysine or arginine. Fish fed high levels of L ‐arginine suffered high mortalities. No significant differences were obtained in the feed efficiency ratios (FER, g gain g^?1 feed) of fish fed graded lysine, although the values tended to increase as the dietary lysine level was increased up to the requirement level. In contrast, in the arginine experiment, significant differences in FER of fish among treatments were obtained; the highest FER was observed in fish fed the diet containing an optimum arginine level. On the basis of the growth response, survival, and FER, the lysine and arginine requirements of juvenile Asian sea bass were estimated to be 20.6 g kg^?1 dry diet (4.5% protein) and 18.2 g kg^?1 dry diet (3.8% protein), respectively. These data will be useful in the further refinement of practical diet formulations for the Asian sea bass.     

Effects of dietary lipid source on reproductive performance and tissue lipid levels of Nile tilapia Oreochromis niloticus (Linnaeus) broodstock

Nile tilapia were fed diets supplemented with one of the following lipid sources at 5% level: cod liver oil, corn oil, soybean oil, a coconut oil-based cooking oil or a combination of cod liver oil and corn oil (1 : 1). The control diet had no lipid supplement and tad fish meal as a sole protein source. A diet with soybean meal as a protein source was also tested. The number of females that spawned, spawning frequency, number of fry per spawning, and total fry production were increased at varying degrees by the supplemental lipid sources except for the cod liver oil. Fish fed the soybean oil diet tad the best overall reproductive performance over a 24-week period. Fish fed the cod liver oil diet had the highest weight gain but the poorest reproductive performance. The suplemental lipids significantly increased crude fat levels in the liver and ovaries. Both males and females Ld the cod liver oil diet had the highest levels of fat in the liver and muscle. The ratio of total n-6/n-3 fatty acid in the liver, ovaries and testes was influenced by the supplemental lipid sources. It was highest in fish fed either the soybean oil diet, the corn oil diet, or the soybean meal diet and lowest in fish fed the control diet or the cod liver oil diet.     

Growth of Nile tilapia (Oreochromis niloticus L.) fed with diets containing graded levels of green algae ulva meal (Ulva rigida) reared in geothermal waters of southern Tunisia

The use of green algae ulva meal (UM) (Ulva rigida) was evaluated as a replacement for soybean meal in a practical diet formulated to contain 28% crude protein, 7.50% lipid and 15 kJ gross energy g^?1. Soybean meal was replaced by 0%, 10%, 20% and 30% of UM (diets U₀, U₁, U₂ and U₃, respectively). The feeding experiment was carried out in an open circulation system. Each diet treatment was applied to triplicate groups of 30 fish (21.37 ± 0.193 g average wet weight) per tank (400 L) arranged in a completely randomized design. The fish were hand fed to satiation four times daily between 07.00 and 18.00 hours for 75 days. There were no significant differences (P > 0.05) in growth performance among fish fed with diets U₀, U₁ and U₂. However, fish fed diet U₃ had significantly lower growth (P < 0.05) than those fed diets U₀, U₁ and U₂. Fish fed the control diet (U₀) and diets including 10% and 20% UM had significantly (P < 0.05) better daily weight gain, relative growth weight, specific growth weight and protein efficiencies ratio than those fed with diet U₃. Feed conversion ratio increased with increasing UM content, but only the value found in fish fed with diet U₃ differed significantly (P < 0.05) from all other treatments. Survival rates ranged between 91.11% and 93.33%. No feed‐related mortality was observed during the entire experimental period. Apparent protein digestibility (APD) of diets ranged from 87.06 to 69.91% and was lowest for fish fed with diet U₃. In general, APD values decreased with increasing inclusion levels of UM, explained by the increase of anti‐nutritional factors and high non‐digestible fibre content. Compared to the control diet (U₀), fish fed diets containing high levels of UM had lower levels of carcass lipid and higher levels of carcass moisture. Results show that this product can be included by up to 20% in practical male Nile tilapia diets with no detrimental effects.     

Tryptophan requirement of juvenile Asian sea bass Lates calcarifer

The dietary requirement of tryptophan for juvenile Asian sea bass (Lates calcarifer Bloch) was studied. The juveniles (mean initial weight, 5.30 ± 0.06 g) were given semi‐purified test diets containing fish meal, gelatin, squid meal, and crystalline amino acids, for 12 weeks. Each set of isonitrogenous and isocaloric test diets contained graded levels of tryptophan. Fish (15 per tank) were reared in 250‐L fiberglass tanks provided with continuous flow‐through sea water at 26°C and salinity of 28 p.p.t. Fish were fed twice daily at a feeding rate of 8% of the body weight day^?1 for the first 4 weeks and at 3.5–2.5% of the body weight day^?1 from 5 to 12 weeks. The experiment was in a completely randomized design with two replicates per treatment. Mean percentage weight gains and feed efficiency ratios were significantly different in fish fed varying tryptophan levels. Survival was 100% in all treatments. On the basis of break‐point analysis of the growth response, the dietary tryptophan requirement of juvenile Asian sea bass is 0.41% of the dietary protein. This information will be useful in further refinement of practical feed formulations for the Asian sea bass.     

Individual variations and interrelationships in feeding rate,growth rate,and spontaneous activity in hybrid tilapia (Oreochromis niloticus × O. aureus) at different feeding frequencies

A 30‐day growth trial was conducted to investigate the individual variations in feeding rate, growth rate, spontaneous activity, and their possible interrelationships in hybrid tilapia (Oreochromis niloticus × O. aureus) reared individually at feeding frequencies of one and two meals daily. Results show that the feeding rate in energy (FRe), specific growth rate in energy (SGRe), and food conversion efficiency (FCE) of fish fed twice a day were significantly higher than that of fish fed only once. However, no significant differences in distance or in time spent swimming were observed between the groups. SGRe was positively correlated with FRe in fish fed only once daily, and SGRe was positively correlated with food conversion efficiency in energy (FCEe) between the two groups. SGRe was only inversely correlated with the distance that fish swam when fed once daily. The results suggest that the individual growth differences of hybrid tilapia could be attributed mainly to variations in FRe, and that the energy costs of spontaneous activity play an important role in the differences at feeding frequency of one meal a day. However, at feeding frequencies of two meals a day, individual growth differences in fish may be caused by variations in FCEe, and energy costs of spontaneous activity have only marginal effects on the differences.     

Nutritional evaluation of treated X’pelon seed (Vigna unguiculata (L.) Walp) in the feeding of Nile tilapia (Oreochromis niloticus)

Legume seed products are used extensively in human and animal nutrition, but high levels of inclusion are often avoided as their secondary compounds can interfere with digestion and absorption of nutrients in the digestive tract. Due to the well-known benefits of some physicochemical treatments on nutritional value, this experiment was completed to assess effects of soaking and heat treatment on the nutritional value of dehulled and hulled X’pelon seeds (Vigna unguiculata (L.) Walp) to Nile tilapia (Oreochromis niloticus) fingerlings. Seeds were soaked for 16 h in a 2 g/kg sodium bisulphate solution in water. Seeds were divided into two lots, being hulled and dehulled. Three heat treatments were used to convert the seeds to meal, being 5 h of hot air flow (70 °C); autoclaving at 119 °C for 30 min to 1.05 kg/cm², and 7 h in a forced air oven at 48 °C. The resultant crude protein (CP) quality of each meal was evaluated by amino acid analysis and by a tilapia feeding study in which fingerlings were fed one of eight diets, each containing 350 g CP/kg of DM, of which seven diets were formulated with 0.80 of CP provided by fish meal and 0.20 by the X’pelon meals and one control diet was formulated with fish meal as the sole CP source. The study encompassed 9 weeks during which fingerlings were fed ad libitum. Chemical and secondary compound analysis of treated seeds showed that heat flow reduced phytic acid by 34.9% and trypsin inhibitors and hemaglutinin decreased by 94.5%, while complete elimination was obtained with autoclaving. Soaking and heat treatment are suitable for partial or complete elimination of the secondary compounds of X’pelon seeds without affecting the content and bioavailability of amino acids, with heat treatment by hot air flow the best. Partial replacement of fish meal with X’pelon meal improved growth and feed efficiency of Nile tilapia, whether the meal was treated or raw.     

Temperature modulates hepatic carbohydrate metabolic enzyme activity and gene expression in juvenile GIFT tilapia (Oreochromis niloticus) fed a carbohydrate-enriched diet

The effects of rearing temperature on hepatic glucokinase (GK), glucose-6-phosphatase (G6Pase) and Glucose-6-phosphate dehydrogenase (G6PD) activity and gene expression were studied in GIFT (genetically improved farmed tilapia) tilapia fed a high carbohydrate diet containing 28% crude protein, 5% crude lipid and 40% wheat starch. Triplicate groups of fish (11.28 g initial body weight) were fed the diet for 45 days at 22 °C, 28 °C or 34 °C. At the end of the trial, final body weight of juvenile at 28 °C (59.12 g) was higher than that of the fish reared at 22 °C (27.13 g) and 34 °C (43.17 g). Feed intake, feed efficiency and protein efficiency ratio were also better at 28 °C. Liver glycogen levels were higher at 28 °C, while plasma glucose levels were higher in the 22 °C group. Significant (P<0.05) effects of water temperature on enzymes activities and gene expression were observed. Hepatic GK activity and mRNA level were higher at 28 °C than at 34 °C. Higher G6Pase and G6PD activity and gene expression were observed at 22 °C. Overall, the data show that juveniles reared at 28 °C exhibited enhanced liver glycolytic capacity. In contrast, hepatic gluconeogenesis and lipogenesis were increased by low temperature (22 °C).     

Evaluation of Nutritive Value of Raw and Fermented De-oiled Physic Nut, Jatropha curcas Seed Meal in the Formulated Diets for Rohu, Labeo rohita (Hamilton) Fingerlings

Rohu (Labeo rohita) fingerlings, were fed de-oiled Jatropha curcas seed meal (DJSM) supplemented diets for 60 days and the effectiveness, if any, on the growth was evaluated. Nine isonitrogenous (35 % crude protein) and isocaloric (4.0 kcal g^?1) diets were formulated of which one was reference diet (RD, fishmeal based control diet) and the other eight were experimental diets prepared by incorporating raw (D1–D4) and fermented (D5–D8) DJSM at 10, 20, 30 and 40 % levels by weight, respectively. Autoclaved DJSM was processed through solid state fermentation (SSF) for 15 days at 37 ± 1 °C by an exo-enzyme producing bacterium, Bacillus cereus Lr.H.23 isolated from the hindgut of rohu, L. rohita. Processing through SSF caused decrease in the contents of crude fibre and anti-nutritional factors, but increase in the levels of free amino acids and free fatty acids. In terms of growth performance, feed utilization efficiency and apparent protein digestibility, fish fed diet D7 containing 30 % fermented DJSM showed the best performance, which differed significantly (P < 0.05) from that of the fish fed diets containing raw DJSM. The results indicated that an inclusion level up to 30 % fermented DJSM replacing 15 % FM in the practical diet for rohu fingerlings can be proposed when compared to the RD. However, further experiments are required to recommend the ingredient for use in industry.     

Nutritive value of dried lactic acid fermented fish silage and soybean meal in dry diets for juvenile catfish, Clarias gariepinus (Burchell, 1822)

Dry diets containing either fish meal (C-FM) or dried fermented fish silage and soybean meal blend (1:1, ww⁻¹) (C-FS) as the sole protein source, were fed to triplicate groups of juvenile Clarias gariepinus (10.8 ± 0.3 g) at 5% body weight per day for 70 days. Catfish fed the C-FS diet showed reduced (P < 0.05) growth rate, feed conversion, protein efficiency and digestibility. Lower amounts of available amino acids in the C-FS diet resulted in inferior nutritive value for catfish growth than in the C-FM diet. Postprandial changes in plasma amino acids showed similar patterns in both diet treatments, but the maximal mean levels attained for the C-FS diet were correspondingly lower and occurred earlier than with the C-FM diet. There were no effects of feeding C-FS diet on the hepatosomatic index but carcass analysis showed that body protein deposition was lower (P < 0.05). Differences in haematocrit, haemoglobin content and liver histology were demonstrated but were not pathological. Lower digestible energy of C-FS diet also contributed to the poor performance of catfish in this treatment. Results of this study indicate that C. gariepinus cannot metabolize protein from co-dried fish silage as efficiently as fish meal protein when used as the sole dietary protein.     

Utilization of copra meal in the formulation of compound diets for rohu, Labeo rohita, fingerlings

Six isonitrogenous (35% crude protein) experimental diets were formulated with raw and soaked de-oiled copra meal substituted for fish meal in the diet at 20, 30 and 40% levels by weight. The tannin content of raw de-oiled copra meal was reduced from 2.4 to 0.9% by soaking it in water for 16 h at room temperature. The response of rohu, Labeo rohita (Hamilton), fingerlings fed these diets for 80 days was compared with fish fed a fish meal-based control diet. On the basis of growth response, food conversion ratio and protein efficiency ratio, the 30% soaked copra meal diet resulted in the best fish performance (P < 0.01). The growth response of the fish was significantly (P < 0.01) affected by both type and inclusion level of the oilseed meal. The growth of fish declined with the increasing level of inclusion of copra meal, irrespective of the type of meal used. The apparent protein digestibilities (APDs) for the raw copra meal were lower at all levels of inclusion in comparison with those for the soaked meals. The highest amount of carcass protein was recorded in the fish fed the diet containing 30% soaked copra meal. The results showed that de-oiled copra meal can be incorporated into carp diets up to 20% in the raw condition and up to 30% in the treated condition without any deleterious effects on growth performance of Labeo rohita fingerlings.     

Hormonal sex reversal of wild-spawned tilapia in India

The effectiveness of methyltestosterone (MT) for sex reversal and growth promotion in Oreochromis mossambicus was studied in culture experiments in India. Wild-spawned fry were treated with 30 μg MT g⁻¹ diet for 30 or 60 days at two feeding levels (initially 20% or 10% of body weight daily). The fish were grown on for 66–96 days after the hormone treatment period in fertilized cement ponds without supplementary feeding. Tilapia treated with MT for 60 days attained an average weight of 29.0 g compared to 18.8 g for untreated fish reared under similar conditions. The percentage of males among the untreated tilapia was 58%, MT treatment for 30 days significantly increased this percentage at the higher feeding level (79% male), but not at the lower feeding level (51%). More than 90% of the tilapia in both 60 day MT treatment groups were male; 3% of all the fish reared showed an intersex condition. The experiments demonstrated that the anabolic and sex reversal effects of MT on tilapia are proportional to the duration of treatment and quantity of hormone administered. The possible application of monosex tilapia culture in tropical countries is noted.     

Effect of feeding pineapple waste on growth performance,texture quality and flesh colour of nile tilapia (Oreochromis niloticus) fingerlings

The study aims to evaluate the effects of pineapples waste on the growth, texture quality and flesh colour of Nile tilapia (Oreochromis niloticus) fingerlings. Fingerlings were fed with four different levels of pineapple waste diets throughout 56 days, which contain a control group (Diet 1) and experimental diets that formulated with 10% (Diet 2), 20% (Diet 3) and 30% (Diet 4) of pineapple waste. The experimental diet was formulated with rice bran, fish meal, soybean meal, vitamin and mineral premix, vegetable oil and binder to attain 32% dietary protein. The results revealed that the formulated fish diet with pineapple waste given the optimum weight gain, weight gain percentage, specific growth rate than the control group, where Diet 4 has shown the highest value (p < 0.05). There were no effects of the pineapple waste diet on the texture quality of the fillet, while only red chromaticity (a*) showed a significant difference (p < 0.05). In conclusion, the addition of pineapple waste can improve the growth rate of Nile tilapia, and the supplementation level of the pineapple waste in the diet was 30% of the total feed formulation.     

Apparent digestibilities and growth experiments with tilapia (Oreochromis niloticus) fed soybean meal, cottonseed meal and sunflower seed meal

Apparent digestibility and growth experiments with three oil seed by-products, soybean meal, cottonseed meal, and sunflower seed meal, were conducted using tilapia ( Oreochromis niloticus ) with an initial average body weight of 93 ± 5 g and 64 ± 1 g, respectively. The diets were formulated on an isonitrogeneous and isoenergetic basis. During the experimental period the fish were fed 1% and 1.5% of their metabolic body weight (kg^0.8) daily in the digestibility experiment and the growth experiment, respectively. Water temperature was maintained at 26.5 ± 1°C. Apparent digestibilities of the components and the diets were determined using an indirect method, i.e. with HCl-insoluble ash as an indicator. Faeces collection was carried out using a sedimentation technique.
Results of the apparent digestibilities showed that the crude protein, crude fat, as well as the gross energy digestibilities of soybean meal (93.0%, 94.6%, and 77.2%, respectively), were better than those of cottonseed meal (79.4%, 83.2%, and 57.9%, respectively) and sunflower seed meal (89.8%, 82.9%, and 49.3%, respectively). With the exception of the crude protein digestibility, nutrient and gross energy digestibilities of the cottonseed meal were found to be better than that of sunflower seed meal.
Growth experiment results indicated that soybean meal diet groups had inferior growth performance and feed conversion in comparison to the fishmeal control diet or the other test diets at an inclusion level of 32% of the digestible protein. Fish fed cottonseed meal diet and sunflower seed meal diet showed a relatively better, but not significantly different performance than did the fishmeal control diet. Supplementation diets with lysine and methionine did not enhance fish performance.     

Growth and body composition of rohu, Labeo rohita (Hamilton), fed compound diet: winter feeding and rearing to marketable size

A 122‐day growth trial was conducted to observe the impact of polyhouse in winter on growth, conversion efficiencies and body composition of fingerling Labeo rohita (7.9 ± 1.1 cm; 4.60 ± 0.18 g). Fish were stocked (1.5 m^?2) in polyhouse and outdoor concrete tanks (250 m²) in duplicate and fed a compound diet [35% crude protein (CP)] to apparent satiation twice daily, at 09.00 and 17.00 hours. A natural photoperiod was maintained during the trials. At the end of the trials, polyhouse‐reared fish produced significantly (P < 0.01) higher values for weight increment, specific growth rate (SGR %), protein efficiency rate (PER), protein productive value (PPV) and better feed conversion ratio (FCR). Polyhouse‐reared fish showed higher (P < 0.01) CP and fat, and lower (P < 0.01) moisture and ash contents in the muscle. In the second part of the study, which also lasted 122 days, polyhouse‐reared young L. rohita (21.7 ± 1.3 cm; 127.8 ± 0.69 g) were raised to marketable size in outdoor earthen ponds (500 m²) at a stocking density of 0.37 m^?2 to examine the effects of feeding traditional feed mixture and compound diet (30% CP) on growth and body composition of fish. Labeo rohita fed the compound diet showed higher (P < 0.01) values for weight increment, SGR (%), PER and PPV, and better (P < 0.01) FCR than those fed traditional feed. Proximate composition of fish muscle showed higher (P < 0.05) CP and fat, and lower (P < 0.05) moisture and ash contents in fish fed the compound diet. The results suggest that polyhouse may be used successfully to culture L. rohita during winter, and that thereafter the fish may be reared in earthen ponds using the compound diet to obtain better production.